In Japan, voice actresses have a niche fan base. There are magazines and websites dedicated to them, and popular voice actresses might parlay that into music singles or photobooks. Aya Hirano, the voice of Haruhi Suzumiya, was able to make the leap from anime and games to mainstream celebrity, appearing on television…
In Japan, Rie Tanaka (Phantasy Star Portable, Shin Megami Tensei: Persona 3) is such a popular voice actress that last year she got her own trading cards. This year, she's getting her own hug pillow cover. Progress!
Some cosplayers make their own costumes. Some buy them. The price range for costumes can go from affordable to totally not.